Thermoplastic composite rocket propellant

Abstract

A process is disclosed by which thermoplastic elastomers may be utilized torepare melt-formable composite rocket propellants. The thermoplastic elastomer is dissolved in a volatile organic solvent, the other propellant ingredients are mixed in, and the volatile organic solvent is evaporated. The dried propellant is melt-formed to final shape by molding or extruding above the melting point of the elastomer. An example of a usable thermoplastic elastomer is a block copolymer comprised of about 5 to about 20 weight percent styrene and of about 80 to 95 weight percent diene. The formed grain can be reclaimed by melting or dissolution in an organic solvent for reuse of the propellant ingredients.

I claim: 
     
       1. A process for utilizing a thermoplastic elastomer as a binder for a composite propellant composition and for forming a solid propellant grain of same, said process comprising: (i) providing a thermoplastic elastomer which consists of hard segments having substantially crystalline properties and soft segments having substantially amorphous properties, said hard segments imparting rigid properties to a solid propellant composition with which it is combined, and said soft segments imparting rubbery properties to a solid propellant composition with which it is combined;   (ii) dissolving said thermoplastic elastomer in an excess amount of a volatile organic solvent;   (iii) adding and mixing an aziridine compound as a bonding agent in said dissolved thermoplastic elastomer to enhance the adhesive bond between the binder material and propellant composition solids;   (iv) continue adding and mixing into said dissolved thermoplastic elastomer, propellant solids including aluminum powder as a fuel element and two different nominal particle sizes of ammonium perchlorate as oxidizer to increase particle packing efficiency;   (v) continue mixing said solids in said thermoplastic elastomer solution to achieve a uniform mixture of said composite propellant composition;   (vi) evaporating said organic solvent from said composite propellant composition to yield a dry solid composite propellant composition free from said volatile organic solvent;   (vii) chopping said dried solid composite propellant composition into pellets;   (viii) placing a predetermined amount of said pellets in a mold and heating to 150° C. to yield a viscous fluid of said solid composite propellant composition;   (ix) pressing said viscous fluid in said mold; and,   (x) cooling said mold and releasing from said mold a formed solid composite propellant grain.   
     
     
       2. The process of claim 1 wherein said volatile organic solvent is toluene and said thermoplastic elastomer is a block copolymer of styrene and a diene, said styrene comprising from about 5 weight percent to about 20 weight percent of said thermoplastic copolymer with balance weight percent of said thermoplastic elastomer comprised of said diene. 
     
     
       3. The process of claim 1 which additionally includes the step of reclaiming said solid composite propellant grain by melting. 
     
     
       4. The process of claim 1 which additionally includes the step of reclaiming said solid composite propellant grain by dissolving in a volatile organic solvent.